The ability to resolve the fine spectral and spatial details on the retina can play a key role in the early diagnosis of vision loss. There is strong evidence linking certain retinal biochemical and physical changes to increased risk of developing vision losses. These preclinical features cannot be observed directly with today's imaging systems.
One proposed solution to the foregoing problems is to use a hyperspectral optical imaging system to measure the fine spectral and spatial features, and then processing and analyzing hyperspectral images of the retina obtained from the hyperspectral optical imaging system. Through hyperspectral imaging, these features would be preclinically detected and spectrally/spatially characterized. This type of phenotyping of lesions would help researchers and clinicians better classify biochemical profile of the disease and/or to detect abnormal cellular structures.
Various proposed approaches to this solution have been demonstrated. Collectively, a fundus imager (which is used to make an image of the retina) combined with spectral encoding optics (which is used to create the spectral signature from the image of the retina) is commonly referred to in this art as a hyperspectral imager system. A flash source is used with such an instrument to collect an image of the retina. This image is then relayed to a Fourier transform hyperspectral imager where the interferometer is set such that there is a separation between the two beams containing the image by rotating an optical element. The two beams are then interfered and the resulting image recorded, encoding one modulation of the full spectrum of the image. The optical element is then rotated a small amount and a second imager is collected using a second flash and this image is recorded, collecting a second modulation. This process is continued until a full set of separations that allow recovery of the desired optical spectrum.
The entire process can take up to several minutes. After collection, the images must be registered to assemble a spatially aligned data set that can then be Fourier transformed to produce a hyperspectral image. For example, U.S. Pat. Nos. 5,539,517, 5,784,162, 6,142,629, 6,129,532, 6,276,798, and 6,556,853 may be referred to for details of optical systems for obtaining Fourier transform spectral images based on a rotationally modulated common path interferometry (also known as a “Barns interferometry”). A major problem for the imagers disclosed is the inability to simultaneously record the entire spectral signature for an imaged area before the eye has moved. Registration is necessary with these imagers because the eye shifts slightly between successive images due to saccades, an involuntary motion of the eye.
The above described instrumentation has a number of significant limitations. Numerous exposures are required and it takes a long time to record a complete spectra. Both spatial and spectral registration are required. It is also necessary to use movable optical elements within the hyperspectral element. The apparatus is rotationally modulated, and provides no control of the spectra or duration of the illumination sources.